Embodiments of the invention relate generally to x-ray tubes and, more particularly, to a method of fabricating x-ray tube components.
Traditional x-ray imaging systems include an x-ray source and a detector array. X-rays are generated by the x-ray source, pass through an object, and are detected by the detector array. Electrical signals generated by the detector array are conditioned to reconstruct an x-ray image of the object.
In general, the x-ray source is in the form of an x-ray tube that includes a vacuum housing enclosing an anode assembly and a cathode assembly. The cathode assembly includes an electron emitting filament that is capable of emitting electrons. The anode assembly provides an anode target that is spaced apart from the cathode and oriented so as to receive electrons emitted by the cathode. In operation, electrons emitted by the cathode filament are accelerated towards a focal spot on the anode target by placing a high voltage potential between the cathode and the anode target. These accelerating electrons impinge on the focal spot area of the anode target. The anode target is constructed of a high refractory metal so that when the electrons strike, at least a portion of the resultant kinetic energy generates x-radiation, or x-rays. The x-rays then pass through a window that is formed within a wall of the vacuum enclosure, and are collimated towards a target area, such as a patient. As is well known, the x-rays that pass through the target area can be detected and analyzed so as to be used in any one of a number of applications, such as a medical diagnostic examination.
In general, only a very small portion—approximately one percent in some cases—of an x-ray tube's input energy results in the production of x-rays. In fact, the majority of the input energy resulting from the high speed electron collisions at the target surface is converted into heat of extremely high temperatures. This excess heat is absorbed by the anode assembly and is conducted to other portions of the anode assembly and to the other components that are disposed within the vacuum housing.
Because of the heat generated in the x-ray tube during operation, it is required that many components in the x-ray tube—such as the anode assembly (target and shaft), cathode cup, electron collector, etc.—be formed of a refractory material that is configured to withstand the high operating temperatures in the x-ray tube. Such refractory materials can include, for example, tungsten, molybdenum, and/or molybdenum alloys, such as molybdenum with additives of titanium, zirconium, and carbon (“TZM”).
Typically, such refractory x-ray tube components are manufactured via a press-sinter-forge (PSF) process, hot-pressing process, or hot isostatic pressing process. Such production processes have inherent drawbacks that cannot be overcome—with such drawbacks including achievable material density and process cycle time, according to the specific process employed. With respect to a PSF process, for example, the separate steps of pressing metal powders to form a compacted “green” shape” or “pre-form,” sintering the pre-form, and close-die forging the pre-form to form a final component, lead to an increased cycle time that is undesirable from a cost and business standpoint.
Therefore, it would be desirable to provide a process for manufacturing refractory x-ray tube components having a reduced cycle time. If would also be desirable for such a process to provide the components as near-net-shape components and as full density/near-full density material components.